The present invention generally relates to a method for fabricating a thermally stable diamond-like carbon film and electronic device containing such film and more particularly, relates to a method for fabricating a thermally stable diamond-like carbon (DLC) film for use as an intralevel or interlevel dielectric in a ULSI back-end-of-the-line (BEOL) wiring structure and electronic structures formed by such method.
Amorphous hydrogenated carbon (a-C:H), also known as diamond-like carbon for its superior hardness, has many useful properties such as chemical inertness, high wear resistance, high resistivity and low dielectric constant (k less than 3.6). For instance, in a paper xe2x80x9cDiamond-Like Carbon Materials As Low-k Dielectricsxe2x80x9d published in Proc. Advanced Metalization and Interconnect Systems for ULSI Applications (1996), by Materials Research Society, Pittsburgh, Pa. 1997, such desirable properties were discussed. DLC films can be fabricated by a variety of techniques including physical vapor deposition or sputtering, ion beam sputtering and DC or RF plasma assisted chemical vapor deposition with precursors of a variety of carbon-bearing source materials. U.S. Pat. No. 5,559,369, assigned to some of the common assignees of the present invention, further discloses diamond-like carbon for use in VLSI and ULSI interconnect systems.
The continuous shrinking in dimensions of electronic devices utilized in ULSI circuits in recent years has resulted in increasing the resistance of the back-end-of-the-line (BEOL) metalization as well as increasing of the intralayer and interlayer capacitances. This combined effect increases signal delays in ULSI electronic devices. In order to improve the switching performances of future ULSI circuits, low dielectric constant insulators and particularly those with k significantly lower than that of silicon oxide are needed to reduce the capacitances. Dielectric materials that have low k values are available, for instance, polytetrafluoroethylene (PTFE) with k value of 2.0. However, these dielectric materials are not stable at temperatures above 300xcx9c350xc2x0 C. which renders them useless during integration of these dielectrics in ULSI chips which require thermal stability at temperatures of at least 400xc2x0 C. DLC materials have been previously considered as a possible low-k dielectric, however, the films have either been found not stable at temperatures above 300xc2x0 C., or have dielectric constants significantly higher than 3.6.
It is therefore an object of the present invention to provide a method for fabricating a thermally stable carbon-based low dielectric constant film that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for fabricating a thermally stable carbon-based low dielectric constant film from a cyclic hydrocarbon precursor.
It is a further object of the present invention to provide a method for fabricating a thermally stable carbon-based low dielectric constant film in a parallel plate plasma enhanced chemical vapor deposition chamber.
It is another further object of the present invention to provide a method for fabricating a thermally stable diamond-like carbon film of low dielectric constant for use in electronic structures as an intralevel or interlevel dielectric in a back-end-of-the-line interconnect structure.
It is still another object of the present invention to provide a method for fabricating a thermally stable diamond-like carbon film of low dielectric constant capable of sustaining a process temperature of at least 350xc2x0 C. for four hours.
It is yet another object of the present invention to provide a thermally stable diamond-like carbon film of low dielectric constant that has low internal stresses and a dielectric constant of not higher than 3.6.
It is still another further object of the present invention to provide an electronic structure incorporating layers of insulating materials as intralevel or interlevel dielectrics in a back-end-of-the-line wiring structure in which at least two of the layers of insulating materials comprise diamond-like carbon film.
It is yet another further object of the present invention to provide an electronic structure which has layers of diamond-like carbon films as intralevel or interlevel dielectrics in a back-end-of-the-line wiring structure which further contains at least one dielectric cap layer as a RIE MASK polish stop or a diffusion barrier.
In accordance with the present invention, a method for fabricating a thermally stable carbon-based low dielectric constant film such as a hydrogenated amorphous carbon or diamond-like carbon film by reacting a precursor gas of cyclic hydrocarbon in a parallel plate chemical vapor deposition chamber is provided. The present invention further provides an electronic structure that has layers of insulating materials as intralevel or interlevel dielectrics used in a back-end-of-the-line wiring structure wherein the insulating material can be a hydrogenated amorphous carbon or a diamond-like carbon film.
In a preferred embodiment, a method for fabricating a thermally stable carbon-based low dielectric constant film can be carried out by the operating steps of first providing a parallel plate plasma enhanced chemical vapor deposition chamber, positioning an electronic structure in the chamber, flowing a precursor gas of a cyclic hydrocarbon into the chamber, depositing a carbon-based low dielectric constant film on the substrate, and heat treating the film at a temperature not less than 300xc2x0 C. for a time period of at least 0.5 hour. The method may further consist the step of providing a parallel plate reactor which has a conductive area of a substrate chuck between about 300 cm2 and about 700 cm2, and a gap between the substrate and a top electrode between about 1 cm and about 10 cm. A RF power is applied to the substrate at a frequency between about 12 MHZ and about 15 MHZ. The heat treating step may further be conducted at a temperature not higher than 300xc2x0 C. for a first time period and then at a temperature not lower than 380xc2x0 C. for a second time period, the second time period is longer than the first time period. The second time period may be at least 10 folds of the first time period. The cyclic hydrocarbon utilized can be selected from either cyclohexane or benzene. The carbon-based low dielectric constant film can be of either a hydrogenated amorphous carbon or a diamond-like carbon.
The deposition step for the carbon-based low dielectric constant film may further include the steps of setting the substrate temperature at between about 25xc2x0 C. and about 325xc2x0 C., setting the RF power density at between about 0.05 W/cm2 and about 1.0 W/cm2, setting the precursor flow rate at between about 5 sccm and about 200 sccm, setting the chamber pressure at between about 50 m Torr and about 500 m Torr, and setting a substrate DC bias between about xe2x88x9250 VDC and about xe2x88x92600 VDC. The deposition process can be conducted in a parallel plate type plasma enhanced chemical vapor deposition chamber. When the conductive area of the substrate chuck is changed by a factor X, the RF power applied to the substrate chuck is also changed by a factor of X.
In another preferred embodiment, a method for fabricating a thermally stable diamond-like carbon film can be carried out by the operating steps of first providing a parallel plate type chemical vapor deposition chamber that has plasma enhancement, then positioning a pre-processed wafer on a substrate chuck which has a conductive area of between about 300 cm2 and about 700 cm2 and maintaining a gap between the wafer and a top electrode between about 1 cm and about 10 cm, flowing a precursor gas of a cyclic hydrocarbon into the chamber, and depositing a diamond-like carbon film on the wafer. The process may further include the step of heat treating the film after the deposition step at a temperature of not less than 300xc2x0 C. for at least 0.5 hour. The process may further include the step of applying a RF power to the wafer. The heat treating step may further be conducted at a temperature of not higher than 300xc2x0 C. for a first time period and then at a temperature not lower than 380xc2x0 C. for a second time period, the second time period is longer than the first time period. The second time period may be at least 10 folds of the first time period. The cyclic hydrocarbon precursor utilized can be either cyclohexane or benzene. The deposition step for the diamond-like carbon film may further include the steps of setting the wafer temperature at between about 25xc2x0 C. and about 325xc2x0 C., setting a RF power density at between about 0.05 W/cm2 and about 1.0 W/cm2, setting the precursor gas flow rate at between about 5 sccm and about 200 sccm, setting the pressure chamber at between about 50 m Torr and about 500 m Torr, and setting a substrate DC bias between about xe2x88x9250 VDC and about xe2x88x92600 VDC. The conductive area of the substrate chuck can be changed by a factor X which leads to a change in RF power by the same factor X.
In still another preferred embodiment, a method for fabricating a thermally stable diamond-like carbon film can be carried out by the operating steps of first providing a plasma enhanced chemical vapor deposition chamber of the parallel plate type, positioning a wafer on a substrate chuck that has a conductive area between about 300 cm2 and about 700 cm2 and maintaining a gap between the wafer and a top electrode between about 1 cm and about 10 cm, flowing a precursor gas of a cyclic hydrocarbon into the chamber over the wafer which is kept at a temperature between about 60xc2x0 C. and about 200xc2x0 C., at a flow rate between about 25 sccm and about 100 sccm while keeping the chamber pressure at between about 100 m Torr and about 300 m Torr, depositing a diamond-like carbon film on the wafer under a RF power density between about 0.25 W/cm2 and about 0.8 W/cm2 while under a wafer DC bias between about xe2x88x92100 VDC and about xe2x88x92400 VDC, and annealing the diamond-like carbon film at a temperature of not less than 300xc2x0 C. for at least 0.5 hour. The method may further include the step of annealing the film at a temperature of not higher than 300xc2x0 C. for a first time period and then at a temperature not lower than 380xc2x0 C. for a second time period wherein the second time period is longer than the first time period. The second time period may be set at least 10 folds of the first time period. The cyclic hydrocarbon precursor can be either cyclohexane or benzene.
The present invention is further directed to an electronic structure which has layers of insulating materials as intralevel or interlevel dielectrics in a back-end-of-the-line interconnect structure which includes a pre-processed semiconducting substrate that has a first region of metal embedded in a first layer of insulating material, a first region of conductor embedded in a second layer of insulating material which comprises diamond-like carbon, said second layer of insulating material being in intimate contact with said first layer of insulating material, said first region of conductor being in electrical communication with said first region of metal, and a second region of conductor being in electrical communication with said first region of conductor and being embedded in a third layer of insulating material comprises diamond-like carbon, said third layer of insulating material being in intimate contact with said second layer of insulating material. The electronic structure may further include a dielectric cap layer situated in-between the second layer of insulating material and the third layer of insulating material. The electronic structure may further include a first dielectric cap layer between the second layer of insulating material and the third layer of insulating material, and a second dielectric cap layer on top of the third layer of insulating material.
The dielectric cap material can be selected from silicon oxide, silicon nitride, silicon oxynitride, refractory metal silicon nitride, where the refractory metal is from the coup comprising Ta, Zr, Hf, W, silicon carbide, silicon carboxide, modified diamond-like carbon and their hydrogenated compounds. The first and the second dielectric cap layer may be selected from the same group of dielectric materials. The first layer of insulating material may be silicon oxide or silicon nitride or doped varieties of these materials, such as PSG or BPSG. The electronic structure may further include a diffusion barrier layer of a dielectric material deposited on at least one of the second and third layer of insulating material. The electronic structure may further include a dielectric on top of the second layer of insulating material, which acts as a RIE hard mask and polish stop layer and a dielectric diffusion barrier layer on top of the dielectric RIE hard mask/polish-stop layer. The electronic structure may further include a first dielectric RIE hard mask/polish-stop layer on top of the second layer of insulating material, a first dielectric RIE hard mask/diffusion barrier layer on top of the first dielectric polish-stop layer, a second dielectric RIE hard mask/polish-stop layer on top of the third layer of insulating material, and a second dielectric diffusion barrier layer on top of the second dielectric polish-stop layer. The electronic structure may further include a dielectric cap layer of same materials as mentioned above between an interlevel dielectric of diamond-like carbon and an intralevel dielectric of diamond-like carbon.